Generally such cartridges include means for supporting the endless loop of tape for travel along a path past one or more access openings defined in the cartridge at which access openings the tape may be engaged by means in a machine to drive it along the path past transducers on the machine also received in the access openings.
Such a cartridge of a type commonly used for radio broadcasting and which can be made to conform to the "Standard" copyrighted in 1976 of the "National Association of Broadcasting" (called NAB herein) for "cartridge tape" is described in U.S. Pat. No. 3,350,025. Cartridges generally of the type described in that patent include a rotatable hub about which a major portion of the tape is coiled, and guides for guiding a minor portion of the tape from the innermost wrap of the coil around one edge surface of the coil, past access openings defined on the cartridge, and then to the outermost wrap of the coil. A tape drive mechanism in a recording and/or playback machine can engage the tape at one of the access openings to pull it from the innermost wrap of the coil past transducers or record and playback heads on the machine received in other of the access openings. The guides in this type of cartridge provide most of the guiding for movement of the tape along a path past the heads on the machine in which the cartridge is mounted. Thus if the cartridge is misaligned with the machine, the tape can be driven along a slightly inaccurate path past the heads, resulting in a phase error in the signal produced by the machine. The tension in the tape varies greatly as the splice for the tape (which splice is adhered to one surface of ends of the tape and has a thickness about equal to that of the tape) moves through the coil from its outermost wrap to its innermost wrap, or as relatively thick portions of the tape (which thick portions are caused by normal minute variations in backing thickness and/or coating weights of oxides or graphite along the tape) move into and out of radial alignment in the coil as the wraps of tape in the coil move relative to each other. Such changes in tension may produce flutter and affect tracking of the tape. Also, in such a cartridge the tape is twisted and pulled from the coil around the side surface of the coil while it is under tension from the tape drive mechanism, which tends to wear the tape at a rapid rate, particularly along its edges, thereby reducing the useful life of the tape in the cartridge.
U.S. Pat. No. 4,268,877 describes an improved cartridge and a method for driving an endless length of magnetizable tape in the improved cartridge past a transducer which will produce a phase error, wow and flutter comparable to that produced by professional reel-to-reel magnetic tape recorders, and which causes significantly less wear on the tape in the cartridge than is caused on the tape in the type of prior art cartridge described above.
The improved cartridge described in U.S. Pat. No. 4,268,877 includes an endless length or loop of tape having a major portion of its length wrapped in a coil around a fixed hub having a central opening. A minor portion of the tape extends from the innermost wrap of the coil through a slot in the hub into the central opening and then around a side surface of the coil to its outermost wrap. If a transducer is positioned in the central opening, and tape is pulled through the slot from the innermost wrap of the coil with the edges of the tape generally coplanar with the edges of the innermost wrap while the tape is guided across the transducer by guides fixed and precisely oriented with respect to the transducer, the phase error of the resultant signal will be very small, especially since the coil will shift axially to provide the best possible alignment between the coil and the guides. Also the surface of the hub supporting the innermost wrap of the coil is defined by annular axially spaced ribs. Such ribs significantly reduce the tension in tape being pulled through the slot as compared to the use of a fixed non-ribbed hub to support the coil by reducing friction between the innermost wrap of the coil and the fixed hub and between adjacent wraps of tape in the coil which move relative to each other as the coil rotates about the hub. Machines which accept such cartridges, however, must have a structure for receiving the magazine with a transducer, guides and a drive mechanism in the central opening of the hub, which structure is substantially different than that of machines presently commonly in use in broadcast studios that utilize cartridges conforming to the "cartridge tape" standards set forth by the NAB. Thus, to use such cartridges it would be necessary for broadcast studios to install new record/playback machines which would be expensive, and would not accept cartridges that do conform to the standards of the NAB which the studio may already have recorded.